Pneumatic rubber tires conventionally have rubber sidewalls which may be subject to considerable flexing and scuffing.
Sidewalls of rubber tires may age somewhat prematurely as a result of (i) weathering due to atmospheric conditions, (ii) fatigue cracking due to continual flexing under operating conditions, and (iii) abrasion due to scuffing.
Rubber sidewall ageing due to weathering may be, for example, a result of exposure to ultraviolet light, ozone and high humidity. Antidegradants are conventionally mixed with the sidewall rubber to counteract such effects. Also, often low unsaturation rubbers such as butyl rubber and EPDM's are included in or mixed with the sidewall rubber for such purpose.
Fatigue cracking of the sidewall rubber is usually due to continual flexing of the tire sidewall as the tire is run under load at service conditions. Such cracking can first initiate and then can propagate, over time, sometimes to an extent that it penetrates deeper into the tire sidewall and, in some cases, may even penetrate the supporting carcass plies. Typically, cis 1,4-polybutadiene rubber is included in the sidewall rubber for a purpose of retarding such cracking.
Tire sidewalls may also prematurely age, or wear, due to scuffing against road curbs or other objects. Rubber is thereby abraded away and a roughened surface results. Excessive scuffing can potentially remove enough rubber so that the underlying and supporting tire carcass may be subject to degradive influences. Often cis 1,4-polybutadiene rubber is included in the sidewall rubber composition to aid in resisting abrasion due to scuffing.
Further, where a tire may be utilized, for example, in an off-the-road service, such as in mine operations and in logging operations, where the tire is run over rough terrain, growth of a crack, or cut, in the sidewall is a consideration. Often a combination of cis 1,4-polybutadiene and natural rubber is used in the sidewall rubber combination to retard cut growth.
A consideration of using trans 1,4-polybutadiene rubber in a tire sidewall composition was made. While utilization of trans 1,4-polybutadiene has been suggested for use in tire treads, (for example, see Japanese Patent Publication Nos. 60-113,036; 62-101,504 and 61-143,453 and U.S. Pat. Nos. 4,510,291 and 5,025,059) utilization of the rubber in a tire sidewall component appears to be novel and the results thereof are believed to be somewhat speculative without evaluation.